XE1202I027 Просмотр технического описания (PDF) - Unspecified

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производитель

XE1202I027

433MHz / 868MHz / 915MHz Low-power, integrated UHF transceiver

Unspecified 

Data Sheet

XE1202

6.5 Reference crystal for the frequency synthesizer

For narrow band applications, where users select the lowest frequency deviation and the narrowest baseband filter,

the crystal for reference oscillator of the frequency synthesizer must have the following characteristics:

Name

Fs

CL

Rm

Cm

C0

∆fs(0)

∆fs(∆T)

∆fs(∆t)

Description

Nominal frequency

Min. value

-

Load capacitance for fs (on-chip) -

Motional resistance

-

Motional capacitance

-

Shunt capacitance

-

Calibration tolerance at 25 °C

-

Stability over temperature range -

(-40 °C to 85 °C)

Aging tolerance in first 5 years

-

Typ. value

39.0 MHz

(fundamental)

8 pF (*)

-

-

-

-

-

-

Table 5 Crystal characteristics

Max. value

-

-

40 Ω

30 fF

7 pF (*)

10 ppm

10 ppm

5 ppm

(*) The on-chip oscillator is implemented in two selectable versions: the first for CL = 8 pF and C0 = 7 pF, and the

second for CL = 8 pF and C0 = 3 pF; the latter will allow a higher amplitude for the internal signal with a slightly

lower consumption.

The electrical specifications given in section 3.2.2 are valid provided the crystal satisfies the specifications given in

table 5.

For less demanding applications in term of signal bandwidth and/or temperature range, it is possible to use crystal

with larger values for ∆fs(0), ∆fs(∆T), and/or ∆fs(∆t). In this case foffset + BWssb should be lower than BWfilter,

where foffset is the offset (error) on the carrier frequency (the sum of ∆fs(0), ∆fs(∆T), and/or ∆fs(∆t)), BWssb is the

single side-band bandwidth of the signal, and BWfilter is the single side-band bandwidth of the base-band filter.

XE1202 can be used with reference crystal operating on its 3rd harmonic at 39.00 MHz. This has 2 consequences:

a) the oscillator start-up time is higher than in fundamental mode; and b) an extra 1.5k to 16k ohm external resistor

has to be placed in parallel to the crystal. In this case, the crystal should have Cload = 8 to 10pF, Rm < 60 ohm, C0

< 7pF.

6.6 Decoupling capacitances

A decoupling capacitance will be placed between each VDD pins and the ground VSS. These five capacitances

must have the following characteristics:

Name

Cci

Typ. value

100 nF

Tolerance

± 10 %

25

D0211-105

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